The present invention relates to an electrorheological fluid damper which is suitable for a slide mechanism used with a machine.
A conventional slide mechanism for a machine, as shown in FIGS. 12 and 13, provides a base 1 and a table 2. FIG. 12 is a sectional side view of the slide mechanism, and FIG. 13 is a sectional view taken along line XIII--XIII in FIG. 12. In the slide mechanism, the table 2 is horizontally moved with respect to the base 1. Square bars 3a and 3b, on which oil type hydrostatic bearings are formed, are mounted on the base 1. Vertically supporting members 4a and 4b are mounted on the table 2. Horizontal bearing pockets h and vertical bearing pockets v are formed in the surfaces of the table 2 and of the vertically supporting members 4a and 4b which are fixed to the table 2. The bearing pockets h and v filled with oil, form oil type hydrostatic bearings, That is, the table 2 is supported through the oil type hydrostatic bearings on the base 1 in such a manner that it is movable parallel relative to the base 1.
A ball thread nut 5 is coupled to the table 2. A housing 7 and supporting bearings 8a and 8b are mounted on the base 1 to support a ball thread bolt 6, which is coupled to an actuator (not shown) such as a servo motor.
As the ball thread bolt 6 is turned, the table 2 is slid forwardly or reversely as indicated by the arrow in FIG. 12, because the ball thread bolt 6 is threadably engaged with the ball thread nut 5. In this operation, the table 2, being guided by the oil type hydrostatic bearings made up of the bearing pockets h and v filled with oil, is moved parallel. The guide mechanism may be a static pressure bearing, rolling guide, or sliding guide as the case may be. The drive mechanism may be a static pressure screw or friction drive as the case may be.
An oil or air type hydrostatic bearing is advantageous in that it is low in viscous friction, and therefore the table 2 can be positioned with high accuracy. However, it is still disadvantageous in that its damping effect is not so high, and therefore it is liable to be adversely affected by vibration. Hence, the table 2 takes a lot of time until it is positioned as required. When the oil or air type hydrostatic bearing is applied to a working machine, chattering is liable to occur with it. Such a disadvantage is applied to a rolling guide.
On the other hand, a sliding guide is high in friction, and therefore it is high in damping effect. However, it suffers from disadvantages that, because of the high friction and the difference between static friction and dynamic friction, stick slip may occur; that is, it is low in positioning accuracy. Furthermore, since its friction is high, the table cannot be quickly moved without great power, which results in the generation of heat.
In order to overcome the above-described difficulties, the present inventors have conducted intensive research on the slide mechanism, and reached the finding that those difficulties can be eliminated by variably controlling the frictional force. In the slide mechanism, the frictional force for obtaining the damping effect is applied to a moving object; however, it is rather difficult to variably control the frictional force applied to the moving object. Therefore, the present inventors have conducted various research on a method of variably controlling the frictional force applied to the moving object, and reached an idea of using an electrorheological fluid whose apparent viscosity changes with the strength of electric field.
However, in order to obtain the viscosity of electrorheological fluid which can be practically used, it is necessary to apply high voltage to it. The use of high voltage naturally limits the material of electrodes to be used, the kind of power source, and so forth, which increases the manufacturing cost. This difficulty may be overcome as follows: That is, the viscous frictional force provided by the electrorheological fluid may be increased without application of high voltage by increasing the contact areas of the electrodes which are in contact with the electrorheological fluid. However, the increasing of the contact areas of the electrodes gives rise to another problem that, if the contact areas of the electrodes were merely increased, then the resultant device would be unavoidably bulky.